Await in Series vs. Promise.all(): When Should I Use Which for Multiple Async Tasks?

Await in Series vs. Promise.all() for Multiple Async Tasks

In JavaScript, there are two common approaches to handling asynchronous tasks: awaiting promises in series or using Promise.all(). This article explores the differences between these approaches, focusing on their timing characteristics.

await in Series

awaiting promises in series involves calling await on each task sequentially, as seen in the second code snippet. This allows the tasks to execute in sequence, which means the following tasks will not start until the previous ones have completed.

Promise.all()

In contrast, Promise.all() takes an array of promises and returns a promise that resolves after all the input promises have resolved, as shown in the first code snippet. This approach allows the tasks to execute concurrently, which can be beneficial for improving performance when tasks can be executed independently.

Timing Differences

The key difference between these approaches lies in their timing. Promise.all() executes all tasks concurrently, meaning they start running simultaneously. This can lead to a faster execution time if the tasks are independent and do not depend on each other. On the other hand, awaiting promises in series executes tasks sequentially, which means the execution time will be the sum of the execution times of each task.

Example:

Consider the following example, where we have three tasks that take 1000ms, 2000ms, and 3000ms to execute:

In this example, using Promise.all() allows the tasks to execute concurrently, significantly reducing the execution time compared to awaiting the tasks in series.

Conclusion

Both approaches have their uses, depending on the specific requirements of your application. If you need the tasks to execute sequentially, await them in series. If the tasks can be executed independently, using Promise.all() can improve performance.

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